1. Field of the Invention
The present invention is directed to an ultrasonic sensor circuit which detects an edge of a material as it passes a specified point and controls a motor to adjust the position of the material in relation to the specified point. In particular, it is directed to an ultrasonic servo controller circuit which is utilized to detect the edge of a web as it proceeds from a pay-off roll to a packaging machine. The controller is used to control a motor which activates a linear actuator that laterally adjusts the position of the pay-off roll as the web is dispensed thereby keeping the web in substantial alignment with the packaging machine.
2. Description of the Prior Art
The food processing industry, as well as several other industries, routinely employ plastic containers having a zipper-type fastening at an open end which is used to seal in the contents of the container. The packaging and sealing of the containers typically takes place in a series of packaging machines which accept the packaging material as a web, formed as a continuous piece, from a pay-off roll.
Since the zipper-type fastening is located along one edge of the web, placing the web on the pay-off roll can be problematic. If the web is placed on the pay-off roll as a continuous piece, there tends to be an excessive build-up of the web material along the edge having the zipper-type fastening. Thus, the diameter of the web along the length of the pay-off roll is not uniform, the end of the roll having the fastening being significantly larger in diameter than the end not having the fastening. The uneven diameter of the pay-off roll which results may likewise prove to be problematic when dispensing the web from the pay-off roll to the packaging machinery.
To prevent this excessive build-up as the web is placed on the roll, the roll is oscillated laterally along its central axis. The amount of overlapping which occurs along the successive edges having the zipper-type fastening is significantly limited as a result.
Oscillation of the roll as the web is placed on the roll creates certain obstacles which must be overcome when the web is subsequently dispensed therefrom to the packaging machinery. Some means must be used to compensate for the unique manner in which the web is placed on the roll. The means of compensation must enable the packaging machinery to receive a steady, non-oscillating stream of web.
It is known to employ infrared servo systems to "de-oscillate" the web as it is dispensed to the packaging machinery. However, such systems are highly complex, expensive and are fraught with practical limitations. The limitations result primarily from the inherent sensitivity which the infrared sensor circuits display to the gauge of the web, the reflectivity of the web material and the presence or absence of web graphics.